IMO using speakers such as the RB41II for LR and C not working depends on how far you sit from them regardless of room size. Room size definitely comes into play with the sub though.
If your main LP is 9-12 ft or so from the front stage then 4" speakers can work well. I use 5 NHT SuperZero 2s with a 50 watt/channel AVR and can hit the upper 90dbs at LP (about 9-10ft) during HT use. My room is small and can be sealed but I don't think that matters for anything other than bass response.
Also, a good sub like the LVR12 would have no problem integrating with speakers crossed at 100hz.
That said, a set of 5 NHT Superzeros would be a better sounding choice than the Klipsch if you plan on any music listening.
Klipsch RF-62II, RC-500, RS-400, SVS PC12+,
Def Tech SC8000
Harman Kardon AVR 1600
PS3, Apple TV, Sharp 70" Qattron